This application claims the benefit of Japanese Application Number 2001-30150 filed Feb. 6, 2001, Japanese Application Number 2001-382112 filed Dec. 14, 2001, Japanese Application Number 2002-22430 filed Jan. 30, 2002 and Japanese Application Number 2002-27099 filed Feb. 4, 2002, the entirety of each of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a veneer lathe including a roller bar for cutting out thin wood sheets (hereinafter called xe2x80x9cveneersxe2x80x9d) from a log.
2. Description of the Related Art
The applicant of this application previously proposed a veneer lathe described in Japanese Patent Laid-Open No. 99507/1999.
This veneer lathe includes a large number of projections disposed round a peripheral surface of a roller bar to a height not protruding from the peripheral surface. The veneer lathe also includes a sliding bearing that is fixed to a knife carriage, which rotatably supports the roller bar, has an arcuate sectional shape opening on the side of a log in a section crossing the shaft centerline of the roller bar, and is so provided as to oppose the log on the opposite side of the log with the roller bar being the center. The veneer lathe further includes a driving source for rotating the roller bar held by the sliding bearing.
The roller bar having the construction described above transmits at least a part of the force necessary for cutting the log. It can also play the role of a pressure bar.
In the veneer lathe described above, the following construction is also disclosed. As shown in FIG. 17, a large number of spiral grooves 57 having a depth of 0.5 mm and a width of 0.5 mm and crossing one another at an angle of 15 degrees in the shaft center line direction are arranged on the peripheral surface of the roller bar 56 in gaps of 3 mm among them in the rotating direction. In this way, diamond projections 58 are disposed on the surface of the roller bar 56 and the surface 58a of each projection is smooth.
FIG. 18 is an enlarged view of a portion encircled by circle 59 shown in FIG. 17. FIG. 19 is a partial sectional view taken along line XIXxe2x80x94XIX in FIG. 18.
As a result, the projections 58 are cut into the peripheral surface of the log on the side where the roller bar 56 is brought into contact with the log. The edge of each projection 58 (on the downstream side of each projection in the rotating direction when the roller bar 56 rotates from above to below in FIG. 18) is caught by the peripheral surface of the log. Consequently, large force can be transmitted to the log in the same way as in the case described above.
However, the veneer lathe described above leaves a large number of fine scratches on the surface of the resulting veneer layer, depending upon the kind of log used. Therefore, the veneer layer produced by this veneer lathe cannot be used for a surface sheet of plywood that is required to be substantially free from surface scratches.
In the case of the veneer lathe using the roller bar shown in FIGS. 17 to 19, when the grooves of the roller bar are clogged with fiber chips of the log, the fiber chips do not easily fall off. As cutting is continued, the grooves are entirely clogged with the fiber chips. In consequence, the roller bar cannot adequately engage the peripheral surface of the log, and cannot transmit a large force to the log.
To solve the problems described above, the present invention provides the following structures.
According to a first aspect of the invention, there is provided a veneer lathe including a knife fixed to a knife carriage for cutting a rotating log. A roller bar is provided at a position for pushing a peripheral surface of the log on the upstream side of the knife in a log rotating direction, and has a plurality of grooves formed on the peripheral surface thereof. Sliding bearings are provided for rotatably supporting the roller bar, and are fixed to the knife carriage. The sliding bearings have, when viewed in a section crossing the centerline axis of the roller bar, an arcuate sectional shape opening to the log, and are arranged so as to oppose the log on the opposite side of the log with the roller bar being the center. A driving source is also provided for rotating the roller bar supported by the sliding bearings. The shape of the grooves in the section crossing the centerline axis of the roller bar is such that an angle between a tangent at a corner of the groove on the upstream side of the roller bar in a rotating direction, which is constituted by a line on the outer periphery of the roller bar, and a first line extending outward from the upstream side face defining the groove, is 130 to 160 degrees. Consequently, the corners of the rotating roller bar on the upstream side of the rotating direction of the grooves cut and anchor into the peripheral surface of the log, and the roller bar can transmit sufficient force for cutting the log. On the other hand, scratches that can be visually recognized hardly remain on the peripheral surface of the log brought into contact with the roller bar.
According to a second aspect of the invention, there is provided the veneer lathe described above wherein the shape of the grooves in a section crossing the centerline axis of the roller bar is such that an angle between a tangent at a corner of the groove on the upstream side of the roller bar in a rotating direction, which is constituted by a line on an outer periphery of the roller bar, and a first line extending outward from the upstream side face defining the groove, is 130 to 160 degrees, an angle between a second line extending outward from the downstream side face defining the groove and the first line is at least 70 degrees, and a depth from the outer peripheral surface of the roller bar to the bottom of the groove is at least 0.05 mm. Therefore, even when wood fibers separated from the log enter the grooves of the roller bar, they can easily fall off from the grooves due to their own weight. Further, the roller bar can stably transmit force to the log, since the corner of the grooves catches the wood fibers.
In accordance with another embodiment, the grooves are spirally disposed in the peripheral surface with respect to the centerline axis, and the grooves are brought into pressure contact with the fiber of the log while the corners of the groove of the roller bar on the upstream side in the rotating direction cross one another. Therefore, it becomes more difficult to visually recognize surface scratches in the resulting veneer.
In accordance with yet another embodiment, the grooves are disposed on the peripheral surface of the roller bar in parallel with the direction of the centerline axis of the roller bar, such that the grooves can suitably correspond to the fiber of the log and can establish the cut-in state. Therefore, driving force can be transmitted reliably.
In accordance with still another embodiment, the grooves and the smooth peripheral surface are alternately arranged on the roller bar in the direction of the centerline axis of the roller bar. Therefore, the roller bar can be kept more stably at the set position by the inner peripheral surface of a holding member.
In accordance with still another embodiment, the sliding bearings are split into a large number and aligned in the direction of the centerline axis of the roller bar, such that exchanging defective bearings and production of the bearing itself can be conducted more easily.
The bearings can also be arranged with gaps between them in the direction of the centerline axis of the roller bar, such that the number of components can be decreased.
In a preferred embodiment, the lathe also includes a holder fixed at one end to the knife carriage in a cantilever arrangement, and coupled to the sliding bearings at the other end thereof, since the bearing is likely to undergo deflection in a departing direction from the log when a large wood chip intrudes between the roller bar and the log. Therefore, excessive force does not act on both the log and the sliding bearings, and their breakage can be reduced.
Preferably, the diameter of the roller bar is not greater than 20 mm, such that pressure can be imparted to the log at a position in the proximity of the knife, and a veneer free from back-cracking can be obtained. On the other hand, the diameter of the roller bar is appropriately at least 12 mm, because as the log becomes thinner with cutting, it does not shrink in the radial direction owing to the pressure.
It is also possible to provide a backup roller facing the log at a position opposite to the knife. The backup roller moves so as to follow the peripheral surface of the log while the diameter of the log decreases with cutting. In this way, driving force can be imparted to the log at a suitable pressing force that does not invite shrinkage of the log even when the log becomes thin with the progress of cutting.
Incidentally, the term xe2x80x9ccenterline axis of the roller barxe2x80x9d represents an imaginary line along the center of revolution of the roller bar.